On the interrelationship of μ-OH bridged dimers, trimers, and tetramers of (en)PtII and their Ag+ adducts

Abstract

[(en)Pt(μ-OH)₂Pt(en)]²⁺, a dinuclear μ-hydroxo bridged complex (with en = ethylenediamine) crystallizes with excess AgNO₃ in high yield as the trinuclear complex [{(en)Pt(μ-OH)₂Pt(en)}Ag](NO₃)₃ (Pt₂Ag, 1) from water. The two halves of the complex are significantly bent (dihedral angle 42.2°) and the three metals form a triangle with the following distances: Pt1⋯Pt2, 2.9729(9) Å, Pt1⋯Ag1, 2.818(1) Å and Pt2⋯Ag1, 2.809(1) Å. The shortness of the Pt⋯Ag distances and the dispositions of the three metal ions strongly suggest that dative bonds from Pt to Ag are responsible for the bending of the two halves of the edge-sharing dinuclear [(en)Pt(μ-OH)₂Pt(en)]²⁺ complex. This scenario appears to be yet another cause of bending of edge-sharing dinuclear μ-OH bridged metal complexes of d⁸ metal ions, adding to those involving Pt⋯Pt bonding, or anion binding, among others. Comparison with related μ-OH dimers of cis-(NH₃)₂Pt^II or (tmeda)Pt^II (tmeda = N,N,N′,N′-tetramethylethylenediamine), which do not display Ag⁺ binding, suggests that the feature of Ag⁺ binding is not common to all cis-bis(am(m)ine) complexes of Pt^II. Interestingly the complete removal of Ag⁺ from 1 does not lead to the μ-OH dimer but rather to the known μ-OH tetramer [{(en)Pt(μ-OH)}₄]⁴⁺.